Presses of this type are already known in which the inflatable chamber is made of an elastically stretchable material, e.g. an elastomer, in the form of a cylindrical sleeve which is deflated so that it is retracted prior to inserting a body to be compressed and which is then inflated so as to cause the chamber to expand, thereby compressing the body. The inside annular wall of the inflatable chamber is in direct contact with the body to be compressed.
During a compression operation it is common for the outer diameter of the compressed body to reduce. In other words, the higher the pressure inside the inflatable chamber, the further the compressed body shrinks in diameter and the further the inside annular wall of the inflatable chamber must correspondingly reduce its circumferential or perimetric length to enable it to follow the change in size of the compressed body against which it is thrust by the pressure.
In practice, the inside annular wall adapts to the reduction in the diameter of the compressed body by forming numerous folds whose size increases progressively as the compression increases.
These folds are a cause of weakness and of rapid deterioration in the material which constitutes the inflatable chamber. It is observed that an important compression effect is exerted on the material at the bottoms of the folds, and that this may lead to rupture of the material due to a crushing effect. In contrast, the sides of the folds, particularly in the proximity of the compressed body, are stretched, and the extension frequently exceeds 50% and may even be greater than the elastic limit of elastomers (400% to 500%). Further, at these folds which grow constantly in size during compression, the pressure stress exerted on the compressed body is not equal to the pressure stress exerted thereon at those zones of the chamber wall which are pressed flat against the compressed body.
Preferred embodiments of the invention provide a press having an annular inflatable chamber made of elastomer and having an annular inside wall which is applied under pressure against a body to be compressed and which does not form folds as the size of the compressed body is reduced due to the pressure.